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DarrylReinsel

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Reply with quote  #1 
Just wondering if you can install a solar unit on a roof and push the air 20' to the basement?
Is there heat loss? What does this do to the efficiency? Also since we are pushing hot air down; Would we want to use a smaller diameter duct, say 4" instead of 6"?
Right now I have been using a 6" hydroponic fan 550 ft.³ a minute through a 6" duct. Temps average 125°.u
Maybe I should use a 5" duct if I am pushing it down for a long distance.

netttech

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Reply with quote  #2 
Being a roofer in my younger years...I avoid deliberately cutting holes in my roof regardless. It's a leak that will likely occur at some point.

That being said...why heat & push air 20' down, when you're passing the space that would benefit the additional heat?

Is the 125 temperature measured at the beginning of the ductwork or the end?? Air tend to lose heat quickly.

You need air volume also along with air temp to be truly effective.

Jeff
Central IL
solardan1959

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Reply with quote  #3 
DarrylReinsel,
Don't cut down on your duct size, just ensure you insulate the duct more to cut down on the heat loss.  This is not as important in areas that will be warmed anyways but very important for unheated areas such as an unheated attic.  A four inch pipe will seriously reduce your flow and raise the temps reducing efficiency by  losing heat out the collector.

Welcome to the site and thanks for the post.
Dan
Garage_Hermit

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Reply with quote  #4 
Darryl,

I would not use a duct at all, unless there was absolutely no other alternative (there usually *is*)

Ducts are a "necessary evil" as they increase pressure and reduce flow.
Ducts are also expensive, require maintenance, and (often) require penetrations in walls & floors, which can be complex and expensive also.

So if U can avoid ducting, do so.

One way to get air to a basement is to use a "whole house fan" (in the basement preferably), that drags air down: remember that the air has to come from somewhere, and go to somewhere else, therefore you would need air intakes and exhausts...

As the air moves around, it will carry any heat with it.  The more heat U require, the more air, and the bigger the fan.

A big fan can produce big discomfort (drafts, noise, chilly breeze) particlarly if your favorite pet gets its head in there...
 
Reading between the lines, you must have a warm attic and a cold basement ?
Your home is maybe suffering from heat stratification...

An attic fan or a ceiling fan might be a good first step to pushing some hot air downwards.

Like Jeff said, make sure in any case that U R not bypassing other areas that would do with the heat - such as a coldish bedroom.

Perhaps read up on the notion of "zone heating" - not all areas of the house need the same temperature: use warm air to warm a bedroom, then exhaust the bedroom air either direct outside, or maybe further down the house, such as to the basement etc.

You can do a lot in a basement with low-grade heat, and apply your prime heat where it works best.

Using ducts - particularly narrow ones - to bring prime heat to a basement might translate into wasting energy - the ducts themselves are inefficient, as stated...

There's a good article on the BIS site  called "a survey of heating options" why not check it out...

G_H



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Seatec

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Reply with quote  #5 
No problem pushing air through 20 ft, just insulate your pipe. I push air through 25 ft of 6 in and cuts it down very little, just get the right fan. On my panel putting hot air in my cement floor it goes through about 60 ft of 5 inch and cuts down the flow from 850 fpm to about 500 fpm, so people are not using a decent fan when they say not to do it.

Wayne
DarrylReinsel

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Reply with quote  #6 
Quote:
Originally Posted by Seatec
No problem pushing air through 20 ft, just insulate your pipe. I push air through 25 ft of 6 in and cuts it down very little, just get the right fan. On my panel putting hot air in my cement floor it goes through about 60 ft of 5 inch and cuts down the flow from 850 fpm to about 500 fpm, so people are not using a decent fan when they say not to do it.

Wayne

This is the fans I use when building the solar air furnaces.

Search eBay
NEW 6" Inch 530 CFM Inline Duct Fan Booster Vent Hydroponic Blower Exhaust M-6
I just don't like the idea of pushing hot air down.
The rood is a metal roof. I have to go through 13' of attic then through the ceiling.
'4' x 8' unit
colinmcc

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Reply with quote  #7 
Perhaps I'm missing something here, but if you are pushing 500+ cfm a minute into the house, which presumably is outside air entering the bottom of your heater, you must also be pushing 500+CFM of air out of your house through cracks, windows etc.. Or, are you also returning air from inside the house into the bottom of your heater?
gbwillson

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Reply with quote  #8 
colinmcc-

You are correct in that an equal amount of air is exchanged. But it is rarely outside air except in perhaps warmer climates or commercial HVAC systems for fresh air exchange. Trying to warm frigid air to room temperature is difficult. Heaters can warm the incoming air as much as 60 degrees or more. In my case, I take cold 55˚F air off the basement floor and replace/exchange it with warmed air that has passed through my heater. The effect of exchanging cold air with warm can have a dramatic effect on the comfort level in a home.

Greg in MN
colinmcc

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Reply with quote  #9 
Hi Greg, I was commenting on DarrylReinsel's original post where he implies that he is using/plans on using one pipe and one fan,  hence my concern.

I agree with you that 2 pipes and 2 fans is the way to go![smile]

Colin
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